Switchless safety arrangement for presses



Aug. 25, 1953 c. J. MEYERS SWITCHLESS SAFETY ARRANGEMENT FOR PRESSES Filed April 2, 1949 IIIIIIP INVENTOR. 6/49155 J. MYERS BY it, '76

ATTOKP/VEVJ' Patented Aug. 25 1953 SWITCHLESS SAFETY ARRANGEMENT FOR PRESSES 4 Charles J. Meyers, Los Angeles, Calif., assignor to Tubing Seal-Cap, Inc., Los Angeles, Calif., a corporation of California Application April 2, 1949, Serial No. 85,238

8 Claims.

In mass production of articles fabricated with presses, a considerable expense is involved in the manufacture and maintenance of the die members arranged to fabricate the different articles. Also, such die members require a relatively long period of time to manufacture by highly skilled toolmakers. In the event that the die members become damaged in use, the presses remain idle for a considerable period of time during which the activities of press operators and other personnel is interrupted.

It is therefore important that the die members be protected from damage.

Usually the die members are harmed due to the failure of the fabricated article to move from the die member after an operation has been performed thereon by such die member; in such case, the next succeeding article fed to the same die member, being stacked on the first article, results in damage to the die member for such die members are intended to accommodate articles of, for example, predetermined thickness only.

In the past, in order to disable the press when such stacking of articles between die members occurs to prevent resulting damage to such die members, micro switches and the like have been placed adjacent the article and arranged to be actuated to disable the press when such stacking occurs; for example, when an article is not correctly positioned with respect to the die members.

Such switches, although satisfactory for a relatively short period of time, are subject to become out'of order, since, as is usual, such article is normally coated with a thin coat of oil, a portion of which may eventually flow or seep to the ad,- jacent switch to serve ultimately as a carrier of dirt and foreign particles with the ultimate result that such switches fail in a relatively short period of time.

It is therefore one of the importantobjects of the present invention to provide an improved safety arrangement for presses characterized by the fact that the control element for disabling the associated press is switchless in character. Another object of the present invention is to provide an improved safety arrangement for presses, adapting for that purpose a novel control circuit of longer life than other circuits used heretofore for the same purpose.

Another object of the present invention is to provide an improved safety arrangement for presses characterized by the rugged nature thereof for assuring continued operation of the press for a longer period of time.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawing in which the figure is a schematic representation of the electrical and mechanical elements of a system embodying features of the present invention.

Referring to the figure, a solenoid coil I0 is connected in a phase shifting circuit in the grid circuit of a thyratron type of tube II. The solenoid I0 has associated therewith a movable core member IDA which is mounted on an operative member |2 of the press, the member i2 being in a predetermined position spring biased against the stop 2|B when a work piece 29 is properly positioned between the die members 2|, 22. In the event that the work piece 28 is not properly positioned, the phase of the voltage to the control grid of the thyratron tube II is such that the tube fires (when simultaneously switch 24 is closed) to energize the relay winding l5. This relay winding I5, in turn, controls the energization of the motor 25 driving the press. Or, such switch |5A associated with relay winding l5 may effect energization of other control elements such as brakes, clutches, etc., for the same intended purpose of stopping movement of the die member 2| in the event of faults occasioned by.

improper positioning of work pieces between the die members 2|, 22.

The mechanical arrangement shown in schematic form is merely exemplary of others of similar character which may be used.

In the figure the members |2A are in the form of; a -knock-out die arranged to remove a work piece 20 from the die member 2| after an operation has been performed thereon by such die member 2|. The die member 22, cooperating with the die member 2!, remains stationary but the piece 2%)- formed therebetween is automatically moved to an adjacent station by conventional means not shown in the direction indicated by the arrow 26. In order to prevent sticking of such piece 20 to the die member 2|, with subsequent resulting damage to the die member 2|, due to stacking of pieces 20 between dies 2| and 22, the knock-out die |2A is provided. It is noted that the member [2 is pivoted at |2B to the die supporting structure 2 |A which i movable vertically as indicated by the arrow 2 IC; and the knock-out die members |2A are in the form of fingers passing through enlarged apertures in member 2 IA and arranged to engage the annular flange on piece 20 when the die member 2| rises to shed the piece 20 from die 2|. These members |2A are pivoted to the member l2.

This knock-out die member I2 is spring loaded by tension spring |2D and acts to remove the work piece from the die member 2| after a forming operation produced thereby in the event that such work piece tends to stick to the die 2|. In other words, the strength of the spring |2D associated with such knock-out die |2A is normally effective to produce such dislodgement or sheding of the piece 2|] from the die member 2|. In abnormal situations, wherein the work piece 20 remains afilxed to the die member 2|, the spring 22D associated with the knock-out die is not sufiiciently strong to dislodge the work piece 20, with the result that the knock-out die member l2 assumes a position different from its normal position.

In the normal operation of the press, the knock-out die member I2 is spring biased against the stop 2513 when the die 2| is approximately near the end of its vertical or forward travel at which time the switch 24 is automatically closed. It is noted that the core member lilA is mounted to move in accordance with the movement of the knock-out die member l2 while the solenoid is relatively stationary with respect thereto and mounted on member 2 IA.

In the normal operation of the press, the core member lfiA thus assumes a position with respect to the solenoid II] to prevent firing of the tube H; but in abnormal operation corresponding to the situation wherein the knock-out die members |2A still contact a work piece stuck on the die member 2| when the member 2 |A is approximately near the end of its vertical or upward travel to eifect closure of switch 24, the core member IEBA is more closely spaced to the solenoid ii! to effect firing of the tube H. It is noted that such solenoid i2 and movable core iiiA are physically closely associated to the die members 2%, 2|, and that its operation, and the life of its operation, is effected in relatively small degree by oil from the pieces seeping over to the solenoid Iii.

The switch 24, preferably of the micro switch type having a flexible actuating arm 24A operated in synchronism with movement of the main die 2|, may be located at positions remote from the die members 2|, 22 themselves to avoid the seeping of oil thereto. In presses having a plurality of punching or forming stations, only one switch 24 may be necessary in each one of the anode circuits of corresponding tubes The thyratron tube I I has its control grid connected to the junction point of solenoid winding iii and bias resistance 30, the other terminals of the winding Ill and resistance being connected respectively to opposite terminals of the secondary winding of biasing transformer 3 I, the center tap oi such secondary winding being connecte-d to the cathode of device H and to one terminal of the secondary winding of the plate transformer 33. The other terminal of such secondary winding of transformer 33 is connected to the anode of the device ll through the serially connected relay windin I5 and normally open switch 24.

It is noted that only alternating current operating potentials are applied to the elements of device II, and that the firing of device H depends upon the phase of the voltage on the control grid with respect to the phase of the voltage on the anode. This phase difference is controlled in accordance with the position of the movable armature IGA. As outlined hereinabove, in the normal position of the core member HJA with the member l2 in engagement with stop 2|B, the tube H is incapable of being fired; but when work pieces are improperly positioned with respect to the die member 2 l, as, for example, when such pieces tend to stack between the die members 2 22, the core lllA is improperly positioned, with the result that the tube II is fired to cause an energizing current to flow through the winding l5. When such winding I5 is energized, the normally closed contacts ISA of the associated relay are opened to effect de-energization of the motor 25 driving the press associated with the die members 2|, 22.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is tocover all such changes and modifi-- cations as fall within the true spirit and scope of this invention.

I claim:

1. A safety arrangement for presses comprising: a first member movable in accordance with movement of a die member, a second member normally movable to a predetermined position in normal operation of the press but arranged to assume a position other than said normal position when said die member is likely to become damaged, a gaseous discharge device having a control grid and an anode, a source of voltage, a connection extending from said source to said anode for the fiow of space current to said device, a first control circuit incorporating said gaseous discharge device change is arranged to fire in accordance with the difierences in phase shift between its control grid and its anode, said first member being arranged to periodically open and close said connection to said anode, andsaid sec- 0nd member being arranged to control the phase of the grid of said device with respect to its anode in accordance with the position of said second member, and a second control circuit associated with said anode circuit to disable said press when said tube is fired.

2. A safety arrangement for presses comprising: a pair of die members, means arranged to move one of said die members, a discharge device having a control grid and an anode, means controlling said die moving means in accordance with current flowing through said discharge device, means arranged to vary the relative phase of the voltage between the control grid and the anode of said discharge device to vary the current flowing therethrough, the last mentioned means comprising a member movable in accordance with the incorrect positioning of an article between said die members, and means operated in timed relationship with said one die member for interrupting the flow of-current to said discharge device.

3. A safety arrangement for presses comprising: a first member movable in accordance 'with the movement of a die member, a second member normally movable to a, predetermined position in operation of the press, but arranged to assume a position other than said normal position when said die member is likely to become damaged, a

discharge device having a control grid and an anode, a first control circuit incorporating said discharge device energized in accordance with difierence in phase shift between voltages delivered to its control grid and its anode, means whereby said second member is arranged to control the phase of the voltage on the grid of said device with respect to the voltage on its anode in accordance with the position of said second member, a second control circuit associated with said anode circuit to disable said press in accordance with current fiow through said discharge device, and means operated in timed relationship with said first member for interrupting the flow of current to said discharge device.

A safety arrangement for presses comprising cooperating die members arranged to perform an operation on an article, means sensitive to correct positioning of said article, die moving means, a gaseous discharge device having a control grid and an anode, a control circuit including said discharge device and said die moving means for controlling said die moving means in accordance with phase differences of voltages on the control grid and anode of said discharge device, means whereby said first mentioned means is operative to control the phase difference between the voltages of said control grid and said anode, means sensitive to the phase difference between said voltages of the said control grid and said anode for disabling said die moving means, and means operated in timed relationship with said die moving means for interrupting the flow of current to said anode.

5. A safety arrangement for presses comprising: cooperating die members arranged to perform an operation on an article, means sensitive to correct positioning of said article, die moving means, a gaseous discharge device having a control grid, an anode and controlling said die moving means in accordance with phase differences of voltages on the control grid and anode of said discharge device, said discharge device having a cathode, a variable inductance connected in the grid and cathode circuit of said discharge device, said first mentioned means being operative to vary the amplitude of said inductance to thereby vary the relative phase difierence between the voltage on said control grid with respect to the phase of the voltage on said anode, and a control circuit responsive to current flow to said anode connected to disable said die moving means, and means operating in timed relationship with said die moving means for interrupting the flow of current to said anode.

6. A safety arrangement for presses comprising: a first die member, a first inductance element mounted on said die member, a knock-out die member, means movably mounting said knockout die member with respect to said first die member, a second inductance element, means stationarily mounting said second inductance element with respect to said knock-out die member, a gaseous discharge device having a cathode, a control grid and an anode, a control solenoid, a control switch, means connecting said control solenoid and control switch serially with said anode, means periodically operating said control switch in timed relationship with operation of said first die member, said first and second inductance elements being magnetically interrelated to form a variable inductance unit which is variable in magnitude in accordance with the relative spacing of said inductance elements, a source of alternating current connected between said anode and said cathode, a source of alternating current connected between said control grid and. said cathode, and means including said inductance unit for controlling the relative phase of the alternating current appearing on said anode and control grid in accordance with the relative position of said inductance elements.

7. Circuitry for use in presses for preventing damage to die members, a gaseous discharge device having a cathode, a control grid and an anode, a first inductance element, a second inductance element magnetically cooperating with said first inductance element to form an inductance unit, a control solenoid, a control switch, a first source of alternating current, a first serial circuit comprising said first source, said control solenoid, said control switch, said anode and said cathode; a second source of alternating current, a second serial circuit including said second source of alternating current, said inductance unit, said control grid and said cathode, means for recurrently operating said control switch, and means for movably mounting one of said inductance elements with respect to the other inductance element.

8. The arrangement set forth in claim '7 in which said means for recurrently operating said control switch comprises die moving means, and wherein one of said inductance elements is stationarily mounted with respect to a first die member and the other on of said inductance elements is mounted on a knock-out die member which is movably mounted with respect to said first die member.

CHARLES J. MEYERS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,782,360 Lynch Nov. 18, 1930 2,134,933 Smith Nov. 1, 1938 2,358,433 Wolfner Sept. 19, 1948 2,483,450 Wolfner Oct. 4, 1949 2,527,797 Cohen Oct. 31, 1950 

